A top aide to U.K. Prime Minister David Cameron, who helped Cameron draft the legislation behind the county's national Internet porn filters, has been charged with "a potential offense relating to child abuse imagery."

Patrick Rock resigned from his post Feb. 12, after the Prime Minister found out the aide was the target of a child porn investigation. He was arrested the next day.

As part of Cameron's policy unit, Rock worked on the law that subjects all 20 million Internet-connected households in the U.K. to web filters unless they opt out. The "family-friendly" system is supposed to block pornographic images, and child porn in particular. In practice, it's actually censoring a lot more than that, cutting off access to a number of charity, education, and news sites that deal with topics related to sex or drugs.

"There's a growing realization that filters are not perfect and will lead to some over-blocking," a spokesman for the Internet Service Providers Association, the group responsible for the actual implementation of the filters, told the BBC.

Rock was a senior Tory advisor, one of only 3 with his own office at No. 10 Downing Street, but the government is now attempting to deemphasize his role in writing the anti-porn legislation.

"Patrick Rock was one of a number of advisers and officials involved in dealing with this issue – but the work was led by somebody else, and decisions were taken by ministers," a Downing Street spokesman told the Telegraph.

No. 10 is cooperating with investigators, giving them "access to all IT systems and offices they considered relevant."